The invention relates to an x-ray diagnostics generator comprising an x-ray tube and a high voltage transformer, wherein the heating filament of the x-ray tube is connected to one portion of the secondary winding of the high voltage transformer, and wherein a photograph-release (or trigger) mechanism is disposed in the primary circuit of the high voltage transformer. An x-ray diagnostics generator wherein the heating filament of the x-ray tube is connected to one portion of the secondary winding of the high voltage transformer is termed directly heated.
In the case of a generator such as this, the heating transformer and the high voltage transformer are switched on simultaneously; i.e., the heating voltage and the high voltage are simultaneously connected to the x-ray tube. Since, due to the inertia (or lag) of the heating filament, no x-ray tube current flows during the first period after the switching-on operation, virtually no voltage drops occur due to the mains and transformer resistances. The secondary no-load (or open-circuit) voltage is therefor substantially greater than the secondary load voltage. This leads to insulation problems.